This present invention relates generally to flight control actuation systems and, more specifically, to a method and apparatus for a dual actuator control system, containing at least one electromechanical actuator and at least one pneumatic actuator. The present invention concerns actuator systems for controlling flight control surfaces on aircraft, spacecraft, missiles, and other flight vehicles.
Actuator servomechanism systems are used to manipulate flight control surfaces to control flight direction, speed, inclination and other positional adjustments for flight vehicles. The actuator systems have used mechanical, hydraulic, electrical, piezeoelectrical, and electromechanical systems to apply force to the control surfaces. For safety, redundant parallel systems are used to independently maintain control of the flight control surface in the event of failure of one of the actuator systems. One such parallel system is disclosed in U.S. Pat. No. 5,074,495 to Raymond. The hydraulically- and electrically-powered actuators individually are capable of providing full actuation power. This system design does not account for significant variances from the normal operational range of the electrically powered actuator, such as control surface flutter and shockwave conditions. Flutter is oscillatory motion between the vehicle frame and the control surface. Flutter increases as the vehicle approaches resonant frequencies. Shockwave conditions increase control surface loads as the vehicle approaches sonic velocity. To account for the resultant high control surface loads, the actuator systems must be large in size and mass, negatively impacting flight vehicle weight constraints and aerodynamic envelope limitations. Additionally, large flight vehicles traveling at high speeds introduce risks of overloading the electrical actuator from the greater forces needed to manipulate the flight control surfaces in such situations. To address these issues, power-assist systems were developed to amplify the force applied from the main control system and to minimize the control system resistance to movement. An example of such a system is disclosed in U.S. Pat. No. 6,349,900 to Uttley, et al. This actuator system uses an electrical actuator assisted by a control tab mounted on the control surface. This system""s drawbacks are lower output forces than conventional actuator systems, and the excess size and mass added to the flight vehicle from the use of control tabs.
None of the prior art is specifically intended for lightweight, high-speed applications, and some suffer from one or more of the following disadvantages:
a) excessive mass and size.
b) inability to accommodate flutter or shockwave effects.
c) increased cooling requirements.
d) low achievable output forces.
e) inferior aerodynamic envelope conditions.
f) inability to use detected electrical actuator current variations.
As can be seen, there is a need for an improved apparatus and method for a light, small, amplified flight control actuation system, which reacts well to flight extremes, such as high speeds and resonant frequencies, does not require excessive cooling, provides high output forces and adapts to detected electrical actuator current variations.
In one aspect of the present invention, a flight control actuation system comprises a control means operable in response to an input for generating a control signal, an electromechanical actuator responsive to the control signal, for operating a flight control surface, and a pneumatic actuator for assisting the electromechanical actuator by reducing the load on the electromechanical actuator.
In another aspect of the present invention, a flight control actuation system comprises a control means operable in response to an input for generating a control signal, an electromechanical actuator responsive to the control signal, for operating a flight control surface, and a pneumatic actuator for assisting the electromechanical actuator by reducing the load on the electromechanical actuator, wherein the pneumatic actuator initializes when the current in the electromechanical actuator increases beyond a predetermined amperage.
In a further aspect of the present invention, a flight control actuation system for a flight vehicle comprises at least one flight control surface. An electromechanical actuator system is adapted to act on each flight control surface, and a pneumatic actuator system is adapted to produce a force to act on at least one of the flight control surfaces. At least one electromechanical actuator is associated with a distinct one of the at least one flight control surfaces and a controller adapted to produce an electrical signal for controlling at least one of the flight control surfaces. An electrical circuit is connected to the at least one electromechanical actuator which is adapted to receive the electrical signal, to control the position of the electromechanical actuator with the electromechanical actuator adapted to move in response to the electrical signal. The pneumatic actuator system is solely associated with the at least one electromechanical actuator, the pneumatic actuator system comprising a piston, a pressure vessel, an exhaust valve, a pressurization solenoid valve, a check valve, a manifold, a pressure switch, the valves adapted to receive the electrical signal and to route a pneumatic pressure to an actuation device adapted to receive the pneumatic pressure and produce a pneumatic force to continuously actuate the distinct one of the aerodynamic flight control surfaces of the flight vehicle in response to the electrical signal.
In another aspect of the present invention, a method is also disclosed for operating a flight control actuation system, the system being adapted to activate at least one pneumatic actuator in response to at least one signal produced by a control surface actuation signal system for positioning at least one control surface. The method comprises the steps of (a) receiving an input signal in the form of a position demand providing an instruction for deflecting a control surface to a new position and (b) the controller generating a corresponding control signal for operating an electromechanical actuator. In addition the method comprises the steps of (c) receiving a feedback signal in the form of an electrical current measurement at the electromechanical actuator, (d) comparing the electrical current measurement to a predetermined electrical current value, and (e) the controller generating a corresponding pressurization control signal for operating a pneumatic actuator for reducing the load on the electromechanical actuator.
In yet another aspect of the present invention, a method for operating a flight control actuation system comprises the steps of (a) operating a flight vehicle, (b) receiving a flap demand instruction, and (c) comparing the position demand with output from a control surface position sensor. In addition the method comprises the steps of (d) generating an actuator position demand to at least one electromechanical actuator, (e) monitoring the electromechanical actuator electrical current load, comparing the electrical current load with a predetermined electrical current load limit, (f) closing at least one exhaust valve, (g) opening at least one pressurization solenoid valve whenever the electromechanical actuator current is more than the predetermined electrical current load limit, and (g) closing a pressurization solenoid valve whenever the electromechanical actuator electrical current load decreases below the predetermined electrical current load limit.
These and other aspects, objects, features and advantages of the present invention, are specifically set forth in, or will become apparent from, the following detailed description of a preferred embodiment of the invention when read in conjunction with the accompanying drawings.